This invention relates generally to communications and more specifically to communications accomplished via spiral antennas. More specifically, the invention relates to utilizing a spiral antenna design that enhances the security of spiral antenna transmission and reception. With greater specificity, but without limitation thereto, the invention relates to using a linearly polarized, conductor-backed, spiral antenna that alters its polarization vector upon a change in frequency.
A great variety of methods have been used and are used to thwart undesired eavesdropping of communications. One such method, credited to past U.S. screen star Heddy Lamar, is the use of frequency hopping. In a frequency-hopped communication, the signal is broadcast over a specific sequence of channels, varying from one frequency band to another. The receiving station knows a-head-of-time the sequence of channels and the specific time at which the channels will be changed. Accordingly, the receiving station can follow and hence intelligently receive a transmission from the frequency-hopped transmission station. Of course, though, the opposite would occur for an unintended listener that does not have the proposed sequence of channels and the timing of the channel switches. It could thus prove difficult for an eavesdropper to be able to overhear a coherent communication signal as, at best, bits and pieces of the communication would be detected.
To improve the eavesdropping of frequency-hopped signals, broad-band, linearly polarized antennas have been employed. One such antenna, the log periodic, is known however to experience limitations when a frequency-hopped signal changes polarization. In such a circumstance, the log periodic antenna could follow the changes in frequency, but not in polarization.
Although two orthogonal log periodic antennas could be used to further enhance eavesdropping, rapid changes in transmission polarization could severely complicate signal detection and interception. This will be true in most cases because of the usual time delay between a signal impinging upon an antenna and the reception equipment registering a detection. Even if crossed log periodic antennas had frequency sensitivity to all polarizations, a combination of frequency and polarization diversity could cause a signal to fail to register a detection. The eavesdropping party could not follow the changes with sensitive enough equipment to still exclude common noise.
There is therefore a need within the art of communications to provide an enhanced method of communicating that accomplishes both frequency and polarization variation.
The invention provides a method for communicating with a decreased probability of detection by an unintended listening party. The method uses frequency hopping and two substantially identical linearly polarized antennas whose polarization vector is synchronized to frequency. Synchronization of polarization with frequency is accomplished through specifically designed conductor-backed spiral antennas. For these conductor-backed spiral antennas, a change in frequency is synchronized to a change in the polarization vector of the communication signal. Since the receiving station will be programmed to alter its reception frequencies in accordance with those being transmitted, the second spiral antenna will automatically change its polarization upon making these frequency changes. A rapid change of polarization increases the difficulty in detecting and intercepting the communication by parties for whom the message was not intended.
Accordingly, it is an object of this invention to provide a communication method for enhancing the security of communications or, put another way, for frustrating the attempts of eavesdroppers from overhearing communications not intended for them.
A further object of this invention is to provide a communication method that employs both frequency hopping and polarization changing to enhance the security of communications utilizing this communication method.
Yet another object of this invention is to meet the above, objects in a simple way.
Still a further object of this invention is to provide a communication method that meets the above objects and that uses spiral antennas.
Other objects, advantages and new features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.